1. Field of Invention
The present invention relates to a disposable childproof lighter, and more particularly to an ignition unit for a disposable childproof lighter, wherein a striker wheel must be driven by two driving wheels to rotate, so as to prevent the disposable childproof lighter from being ignited accidentally or by children.
2. Description of Related Arts
Nowadays, both U.S. government and U.S. Consumer Product Safety Commission demand a safety device in every cigarette lighter including the disposable lighter to prevent unwanted ignition accidentally or by a child. As it is known that the disposable lighter is common and relatively cheap, it is impossible to incorporate with expensive and complex safety device that highly increases the cost of the disposable lighter. In order to minimize the manufacturing cost of the disposable lighter employed with the safety device, one of the most common disposable safety lighter is the driving wheel type disposable safety lighter. This type of disposable lighter comprises a pair of driving wheels for driving the striker wheel to rotate in order to generate sparks, wherein the driving wheels normally run idle when the driving wheels are physically disengaged with the striker wheel.
For example, U.S. Pat. No. 5,547,370, owned by Hwang, discloses a wheel axle mounted between two upright supports at the top of a butane wheel, two driving wheels mounted around the wheel axle and disposed in contact with a spring-supported flint below and turned by the driving wheels through the wheel axle to strike the spring-supported flint in producing sparks. The wheel axle is made of polygonal cross section, having two round rods at two opposite ends loosely inserted into a respective axle hole on each upright support so as to ensure a better connection between the striker wheel and the wheel axle.
Since the dimension of the driving wheels are not produced precisely for minimizing the manufacturing cost of the disposable lighter, there is always a clearance between the driving wheel and the striker wheel. The clearance is supposed to provide a gap that the driving wheels can rotate loosely around the axle in such a manner that the driving wheels are run idle around the axle. However, the clearance also provides a gap that the driving wheels can axially loose such that the driving wheels may not perfectly engage with the wheel axle of the striker wheel in order to provide an optimum mutual friction therebetween for ignition. Furthermore, in order to ignite the lighter, a downward force must applied on the driving wheels for engaging the striker wheel. In fact, due to the contacting surface between the driving wheel and the striker wheel, the disposable lighter is somewhat difficult in operation.
Another example, U.S. Pat. No. 6,220,853, owned by Luo, discloses a striker wheel coaxially sandwiched by two driving caps and a pair of driven gear elements coaxially mounted at two sides of the striker wheel respectively, wherein the driving caps are arranged to engage with the driven gear elements respectively to drive the striker wheel to rotate when a downward force is applied on the driving caps. In other words, the driving caps are run idle at a normal position. However, the each of the driving caps has an outer circumferential knurling surface so that the child is able to strike the driving caps on a floor to engage with the driven gear elements and to rotate the striker wheel.